U.S. Pat. No. 2,820,768 (Fromont) discloses that transparent soap can be made by mixing and heating to a temperature of 100 to 120.degree. C. a transparent alkali metal soap with the reaction product of a fatty acid containing no less than 18 carbon atoms with excess triethanolamine. The soap preferably contains approximately 30% castor oil to improve transparency. Ricinoleates obtained from castor oil were found to dissolve fatty acid salts such as stearates, thus inhibiting crystallization of the soap on cooling.
U.S. Pat. No. 3,793,214 (O'Neill et. al.) discloses that transparent soap bars may be made by neutralizing a mixture of saturated fatty acids and C5 to C18 branched chain fatty acids with a neutralizing agent comprising a sodium compound and an alkanolamine, preferably, triethanolamine. The neutralizing compound contains sufficient sodium compound to neutralize at least 40 percent of the fatty acids. The neutralizing agent also contains sufficient alkanolamine to provide 15 to 45 weight percent of free alkanolamine in the final soap bar composition. The soap contains from 10 to 20 parts of branched chain fatty acid for each 100 parts of soap. Examples of suitable branched chain acids are trialkyl acetic acids commonly known as neo-acids, and 2-ethylhexanoic acid. In the preparation of the bars disclosed, the fatty acids are heated with sodium hydrosulfite to a temperature of 130 to 210.degree. F. (54 to 99.degree. C.) with stirring until homogeneous, and to this are added a pre-blend of the neutralizing agent and water. O'Neill et. al. also disclose that other components, e.g., preservatives, antioxidants, colorants and perfumes may also be present in the formulation. Following the neutralization step, the other components are then added, the mixture is stirred until homogeneous, and it is then poured into molds to cool and form soap bars.
U.S. Pat. No. 4,290,904 (Poper et. al.) discloses that a transparent soap may be made by saponifying a fatty oil, preferably, a mixture of tallow, coconut and castor oils, with caustic soda, water and a polyhydric alcohol. The soap also contains a tetrakis (hydroxyalkyl) ethylenediamine, which may be added either before or after saponification. Additional surfactants to increase foaming and to stabilize the foam, such as amine oxides and alkyl diethanolamides, are desirably added. Other components that may be added include chelating agents, colors, antioxidants and perfumes.
U.S. Pat. No. 4,468,338 (Lindberg) discloses that a transparent soap bar that does not lose its transparency or otherwise darken over time can be formulated from a mixture of alkali metal and triethanolamine salts of C6 to C18 fatty acids, citric acid or one of is alkali metal salts, an alkali metal metabisulfite and water. The fatty acids have an iodine number between 8 and 15.
U.S. Pat. No. 4,758,370 (Jungermann, et. al.) discloses a process for the continuous production of transparent soap. In their process, a mixture of fatty acids, which may include coco fatty acids, stearic acid, oleic acid, ricinoleic acid and other acids, is blended in a first storage tank. Sodium hydroxide solution, which may or may not contain other agents such as triethanolamine, is maintained in a second storage tank. The contents of the two tanks are blended together in a heated, stirred tank reactor at precise stoichiometric ratios to produce a composition which when placed in molds and cooled, hardens to a transparent soap bar. Jungermanri et al. claim the benefit of speed, easier control, and the production of a lighter, more uniform product. They also disclose that inclusion of materials such as antioxidants, BHA, BHT, tocopherol, tocopherol acetate, sodium metabisulfite, chelating agents EDTA and DTPA, isostearic acid, and neo-decanoic acid may be added without adversely affecting the primary characteristics required.
U.S. Pat. No. 5,310,495 and European Patent 0335026B1 (both to Hill, et. al.) disclose transparent soap bars made from carefully controlled compositions. These patents disclose compositions which comprise a mixture of alkanolammonium and alkali metal C12 to C22 fatty acid salts, the mole ratio of these being from 0.1 to less than 1.0. A liquid solvent system comprising water and triethanolamine is also present, the weight ratio of these being from greater than 0.25 to less than 1.0. The weight ratio of total fatty acid salts to solvent must range from greater than 0.2 to less than 1.0. While these patents suggest that unsaturated soaps give bars with a characteristic yellow color, they state that the soaps may contain unsaturation in accordance with commercially acceptable standards, though excessive unsaturation is normally avoided.
Philippine Utility Model 8018 (Dy Dumalasa, et. al.) teaches a transparent soap bar made from low iodine value fatty acids. Butylated hydroxy toluene (BHT) is added to the soap formulation to retard discoloration. The fatty acids used in this soap include 2-ethyl hexanoic acid, topped coconut fatty acids, triple pressed stearic acid and lauric acid.
Disadvantages of the soap bars produced according to the above disclosures is that the soaps exhibit varying degrees of clarity , color and color stability. Furthermore, the soaps of the prior art tend to discolor to varying degrees on aging. This discoloration is especially pronounced at the higher temperatures encountered in warm climates where air conditioning is less common. Furthermore, the soap bars of the prior art tend to irritate sensitive skin.
Accordingly, it is an object of the present invention to provide a soap bar of exceptional clarity and low color.
A further object of the present invention to provide a clear, colorless soap bar which resists discoloration on aging.
Yet a further object of this invention to provide a soap bar that can be made from fatty acids that are entirely plant-derived.
In another object of the present invention there is provided a clear, colorless soap bar which is sufficiently mild to the skin to permit its regular use by individuals with sensitive skin, for example, infants.